Audio bridge circuits which are well known in the art comprise many different circuit configurations. In general, prior art audio bridge circuits consist of a pair of operational amplfiers having respective inputs so connected to receive an input signal which is then amplified and appears across a pair of floating differential output terminals. A load, such as a speaker is connected to the output terminals. The signal developed across the load is swung in both a positive and a negative direction in order that maximum output power is achieved. An example of a prior art audio bridge circuit is illustrated in volume 1 of the magazine "Electronic Design" published Jan. 4, 1978 at page 125.
Some contemporary monolithic integrated audio bridge circuits suffer from several disadvantages. For example, most bridge circuits require many external components, such as capacitors. Thus, not only are extra external pinouts required, but the number of external components is also increased, which in turn increases the cost of the circuits.
Another disadvantage of some contemporary audio bridge circuits is that, due to the high gain of the circuit, large offset voltages may appear across the output terminals. If a speaker is connected to the output terminal, as would be a typical application, the offset voltage will produce a large current through the speaker which causes unsymmetrical clipping of the input signal as well as large power consumption. Thus, it is important to reduce this offset voltage to overcome the aforementioned disadvantages.
Still further, some contemporary prior art audio bridge circuits produce a noise "thump" at both turn on and turn off of the circuit.
Hence, a need exists for a monolithic audio bridge circuit that requires a minimum of external components wherein the offset voltage appearing across the output terminals thereof is severely reduced or eliminated.